6.5  Neurons and Synapses

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Essential Idea:

Neurons transmit the message,

synapses modulate the message


  • Neurons transmit electrical impulses
  • The myelination of nerve fibres allows for saltatory conduction
  • Neurons pump sodium and potassium ions across their membranes to generate a resting potential
  • An action potential consists of depolarization and repolarization of the neuron
  • Nerve impulses are action potentials propagated along the axons of neurons
  • Propagation of nerve impulses is the result of local currents that cause each successive part of the axon to reach the threshold potential
  • Synapses are junctions between neurons and between neurons and receptor or effector cells
  • When presynaptic neurons are depolarized they release a neurotransmitter into the synapse
  • A nerve impulse is only initiated if the threshold potential is reached


  • Secretion and reabsorption of acetylcholine by neurons at synapses
  • Blocking of synaptic transmission at cholinergic synapses in insects by binding of neonicotinoid pesticides to acetylcholine receptors


  • Analysis of oscilloscope traces showing resting potentials and action potentials